Bad CD Unit or Bad Starter?
 

I just got back from trying to help a friend with his '78 targa. It seems it died while he was driving so I went with him to check things out. We first checked for spark and there was none. So I recommended that we take the coil from my car and test again to see if this is the problem. I was thinking coil or CD unit. After switching out the coil the car would not even turn over? Was sup with that! I suggested to him that we try the CD Unit but as it was I was making things worse so he opted to not try the CD unit and have it towed to a mechanics.

Does anyone know what might have caused the starter to not turn over once we were just trying to replace the coil? The only thing I could think of is that we didn’t disconnect the battery and that we might have burned something. Other than that I’m spoofed.

Sounds like a bad CD unit to me.

Any ideas on this one?

I believe the starter should still crank, even with a bad CD unit.

Bad ground(s).

Sounds like you have two problems.

First, the engine should crank with or without a good or bad CD.

Next, if the CD is a Bosch, it should buzz. If so, then check for a
good spark. If no spark, a bad coil is possible but rare. Check
for a good input signal to the CD with an ohmmeter, from the
distributor. Check all +12v and grounds.

Check out the website Systemsc.com (Diagnostics) for some
troubleshooting hints.

Good luck
Loren
Systemsc.com

The ignition problem and the starter problem are independent. I'm with Doug. Clean the grounds. That's likely to help the starter problem, but the ignition problem is something else. Wiggle the two square connectors in the engine compartment.

The ignition and cranking circuit do have something in common... the battery.

You may have a dead alternator and the car was operating on the battery until it fell below operating voltage. Maybe even a poor battery connection. This is just a guesstimate.

Hope this helps,
Sherwood Lee
http://members.rennlist.org/911pcars

Thats whats got me confused. It cant be that coincidental, can it? Five minutes before the coil swap she was turning over fine.

I thought about that as well and the cockpit gauge read that the battery was fully loaded. But did turn quickly to "0" when the key was turned. With no audible clicking sound from the starter. Is that normal?

The CD unit was definatly not buzzing and that was my next step after trying the coil but the owner got spooked and opted to call the tow truck.

Im just bummed because It seems that I made this guys problem worse and that hes going to go thru the whole hassel of calling a tow truck ($$$$).

Any other thoughts would be appreciated. The car hasn't been picked up yet and I still might have a chance to save face.

"I thought about that as well and the cockpit gauge read that the battery was fully loaded. But did turn quickly to "0" when the key was turned. With no audible clicking sound from the starter. Is that normal?"

Simon,
No, that's not normal. An unloaded, but partially discharged battery may indeed read 12+ volts. It's what happens when a load is placed on the battery that counts. Think of the cranking capacity of 8 AA batteries. Unloaded, the 8 AA's connected in series = 12 volts. However, an attempt to rotate a starter motor with this wimpy group would barely warm a conductor. Under normal conditions, the battery should remain above 9 volts while cranking. Typical engine operation voltage should be around 14 volts (if the alternator is working).

If you want to attempt a face-saving maneuver, offer to swap your battery for his (assuming your battery is fine). Maybe this will work. The price is right at this point. BTW, don't screw it up. Positive cable to positive post, etc.

But then again, that's JMO, I could be wrong.
Sherwood

Thanks for all the replies.

The tow truck beat me to it so I'll have to let you guys know how it all turns out. I think Sherwood hit the nail on the head and it was just coincidental that it (battery) went dead while I tried to swap out the coil.

Simon,
I hope your friend sees your efforts as trying to assist rather than being the cause of his car's demise.

have a nice weekend,
Sherwood

The funny thing is that I just meet the guy. He broke down and had always seen me wrenching on my 911 so they (him and his wife) decided to come by and ask for some assistance. Unfortunatly it didnt get them back on the road. :(

Imagine my puzzeled look when the coil was swaped out and instead of the motor fireing up there was dead silence. :eek: